It isn’t an IO Board, it’s an “Oh Eye” board: sixteen 10-bit analog inputs. It makes it easier to use the Pi as part of a special purpose appliance or musical instrument. The analog inputs are via two MCP3008 chips connected to the Raspberry Pi’s hardware SPI interface. The use of this ADC chip with the Pi is common and well documented. You may ask: “isn’t 16 channels of analog input a little overkill?” To which I would answer: yes it is, except when it isn’t.
There’s also a larger version of the Oh Eye that has a few digital inputs and other interfaces pulled out to headers.
A Mess of Inputs
Once you’ve done a number of projects with a lot of potentiometers or analog sensors you’ll appreciate the handiness of the convenience headers. When you’re using analog inputs you are always running three wires to everything: power, ground, and signal.